Finding the optimal tidal volume in acute respiratory distress syndrome

Pellegrini, M., Del Sorbo, L. & Ranieri, V.M. Finding the optimal tidal volume in acute respiratory distress syndrome. Intensive Care Med (2024). https://doi.org/10.1007/s00134-024-07440-5

Abstract:

Severe hypoxemia, alveolar infiltrates, and histological damage due to lung inflammation define acute respiratory distress syndrome (ARDS). The optimal tidal volume (VT) in ARDS patients is critical for minimizing ventilator-induced lung injury (VILI). While low VT (6 ml/kg predicted body weight, PBW) is the standard, recent evidence suggests that tailoring VT to individual patient characteristics, including driving pressure (ΔP) and respiratory system compliance (CRS), may improve outcomes. This article reviews the evolution of VT recommendations and explores the impact of ΔP, PEEP, and regional lung mechanics on ventilatory management in ARDS.

Keywords:?ARDS, tidal volume, ventilator-induced lung injury, driving pressure, compliance of the respiratory system, mechanical ventilation

Introduction:

ARDS is characterized by severe hypoxemia, alveolar infiltrates, and lung inflammation. Initially, high tidal volumes (VT) were used to normalize arterial blood gases, but this approach increased lung damage and mortality. The ARDS Network trial demonstrated that low VT (6 ml/kg PBW) reduced mortality, establishing it as the standard for ARDS patients.

Evolution of Tidal Volume Recommendations:

The ARDS Network trial significantly reduced mortality by using low VT, setting 6 ml/kg PBW as the standard. However, various factors question this fixed cut-off:

1. Lack of clinical studies comparing 6 ml/kg to other VT ranges.
2. Meta-analyses show lower VT (4–8 ml/kg PBW) does not significantly affect outcomes.
3. Many patients on low VT still exhibit signs of hyperinflation.
4. VT based on PBW may be misleading as lung size is reduced in ARDS.

Driving Pressure and Compliance:

Driving pressure (ΔP = VT/CRS) is proposed as a key predictor of outcomes in ARDS. ΔP better stratifies mortality risk compared to VT alone. Reducing ΔP has been shown to improve survival, especially when limited early in mechanical ventilation and maintained over time. ΔP can be calculated using static or dynamic pressures, and efforts to reduce it may involve adjusting VT or increasing PEEP.

Factors Influencing Compliance and ΔP:

PEEP and chest wall elastance (ECW) significantly influence CRS and the interplay between VT and ΔP. Clinical trials comparing high vs. low PEEP strategies have not consistently targeted ΔP, and methods to set PEEP based on physiology vary. Uncontrolled factors such as injury severity, body positioning, airway closure, and hemodynamics also impact CRS and ΔP. Advanced techniques like electric impedance tomography, computed tomography, and pleural pressure estimation may guide personalized VT and PEEP settings for more homogeneous lung ventilation.

Take-Home Message:

While the ARDS Network trial introduced protective mechanical ventilation, recent evidence suggests optimizing VT based on ΔP and considering regional lung mechanics. Clinicians should use protective ventilation principles, accounting for ΔP, CRS, ECW, PEEP, and individual patient characteristics to minimize VILI and improve outcomes.

ACCESS FULL ARTICLE HERE!

Watch this video on "What is Driving Pressure and why is it important?" by Dr. Bellani.

Discussion Questions:

1. How can clinicians effectively balance the use of low VT with the need to minimize ΔP and optimize CRS in ARDS patients?
2. What are the potential challenges and benefits of using advanced imaging and monitoring techniques to guide personalized ventilation strategies?
3. How can future research address the gaps in understanding the optimal VT and ventilation strategies in ARDS?

Javier Amador-Casta?eda, BHS, RRT, FCCM

Interprofessional Critical Care Network (ICCN)

[email protected]

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